The invention relates to a method of producing clipboard or particle board Panels using wood materials and using annual plant materials containing lignocellulose.
In the production of multi-layered plates or panels of lignocellulose-containing materials, it is known to use isocyanate as a binder. The use of isocyanate as a binder for panel products as well as the advantages and disadvantages resulting therefrom are described in the special publication xe2x80x9cIsocyanate as a binder for particle boardxe2x80x9d by Dr. G. Loew, Engineer H. I. Sachs of Bayer AG, from 1977, on page 479. From this it is evident that polyisocyanates adhere onto metals under pressure and heat. As a solution possibility to these problems, the use of liquid separating agents as well as the use of papers, veneers, as well as dust or conventionally adhesive bonded or glued chip cover layers is suggested.
A method for the production of multi-layered panel materials of is a mass of wood chips, wood fibers, or of lignified raw materials, impregnated with isocyanate, is known from the Austrian Patent 270,189. Furthermore it is known from this publication, to use a mixture of isocyanate as well as urea-, melamine-, and phenol formaldehyde resin glue or adhesive as a binder, or for example, to bind the chips in the cover layer with melamine resin and the chips of the middle layer with pure isocyanate solution, or vice versa. By the use of a mixture of the above named binders, a strongly increased moisture resistance and a considerable reduction of the swelling of the panel products upon the penetration of moisture are achieved.
From the U. S. Pat. No. 5,779,955, a method for the production of panel materials is known, in which particles of plant-related products are mixed with isocyanate as a binder as well as water, as the panel material. In order to avoid the problems of the adhering of the mats during the pressing, which problems arise with the use of isocyanate as a binder, the underlayer is covered with a liquid separating agent before the spreading of the mixture. After the spreading process, a separating agent is similarly applied onto the top surface of the laid-down mixture. Thereafter, the hot pressing of the formed body is carried out.
Object of the present invention is to provide a method for the production of multi-layered panel-shaped products, which is utilizable dependent on the availability of raw materials, and the problems arising in the state of the art in connection with isocyanate glued chips are avoided. This object is achieved according to the invention in a method for producing a pressed panel of chips or particles, comprising the following steps:
a) providing a cover layer material comprising chips of wood or a wood-based material;
b) providing a first middle layer material comprising chips of wood or a wood-based material;
c) providing a second middle layer material comprising chips of a non-wood material of annual plants containing lignocellulose;
d) mixing together the first middle layer material and the second middle layer material to form thereof a mixed middle layer material;
e) before or after the step d), applying a first middle layer binder to the first middle layer material and applying a second middle layer binder comprising an isocyanate to the second middle layer material;
f) applying to the cover layer material a cover layer binder that is different from the second middle layer binder and that comprises at least one of an amino polymer resin and a phenolic polymer resin;
g) after the steps e) and f), depositing in sequence a lower layer of the cover layer material having the cover layer binder applied thereon, a middle layer of the mixed middle layer material having the first middle layer binder and the second middle layer binder applied thereon, and an upper layer of the cover layer material having the cover layer binder applied thereon, to form thereof a multi-layered mat body; and
h) pressing the multi-layered mat body to form thereof the pressed chip panel.
The above method according to the invention thus results in a pressed chip panel including a middle layer that comprises a mixture of wood chips and chins of annual plants containing lignocellulose glued with a binder including an isocyanate, and upper and lower cover layers that comprise wood chips glued with a binder including amino and/or Phenolic Polymer.
With the present invention, it becomes possible to produce a panel-shaped product, which consists of a different raw material composition and binder agents or binders in the middle layer and the cover layers. By means of this panel-shaped product, which is referred to as a mixed panel in the following, it is possible for producers, which especially produce chip panels of wood chips, to use the available raw material of annual plants as additional raw material. In a conventionally operating plant for the production of chip panels from wood chips, the existing material preparation can be re-equipped or expanded by an additional straw preparation line. A preparation plant to be set up in such a manner essentially consists of a one- or multi-stage crushing or comminution process, dryer, sifter or sorter, sieve station, as well as a gluing or adhesive applying plant suitable for straw. Depending on the availability of the raw material of annual plants, the proportion of the raw material of annual plants in relation to the raw material wood can be varied in the middle layer. The cover layers of the panel-shaped product according to the invention consist of wood chips, that are glued with amino and/or phenolic plastics. Thereby the problems of the adhesion of isocyanate glued chips onto the plate surfaces during the pressing are avoided. In the inventive method, no additional separating agents or separating layers are necessary, so that additional costs are avoided.
The mixed panel according to the invention with phenolic and/or amino plastic glued wood chips in the cover layers as well as with isocyanate glued straw or straw-wood mixtures in the middle layer comprises a sufficient cold adhesiveness of the spread formed body as well as a good edge stability. Hereby the production process is considerably simplified. By means of this sufficient cold adhesiveness, which is not achieved by pure isocyanate glued straw or wood chips, a stable multi-layered formed body is achieved, which, due to the existing cold adhesiveness, may be more effectively pre-compressed as well as being transportable over the individual transfer areas in the forming or extrusion line to the press inlet without damage of the previously achieved cover layer quality.
In a further development of the idea of the invention it is provided that the middle layer material wood is glued with amino and/or phenolic resins, and the middle layer material of lignocellulose-containing annual plants is glued with isocyanate or mixtures of isocyanate and amino/phenolic resins. A reducing proportion of isocyanate as binder leads to a cost reduction.